Specify a shard iterator using the ShardIterator parameter. The shard
iterator specifies the position in the shard from which you want to start
reading data records sequentially. If there are no records available in the
portion of the shard that the iterator points to, GetRecords returns an empty
list. Note that it might take multiple calls to get to a portion of the shard
that contains records.

You can scale by provisioning multiple shards. Your application should have
one thread per shard, each reading continuously from its stream. To read from
a stream continually, call GetRecords in a loop. Use GetShardIterator to get
the shard iterator to specify in the first GetRecords call. GetRecords
returns a new shard iterator in NextShardIterator. Specify the shard iterator
returned in NextShardIterator in subsequent calls to GetRecords. Note that if
the shard has been closed, the shard iterator can't return more data and GetRecords returns null in NextShardIterator. You can terminate the loop when the shard
is closed, or when the shard iterator reaches the record with the sequence
number or other attribute that marks it as the last record to process.

Each data record can be up to 50 KB in size, and each shard can read up to 2
MB per second. You can ensure that your calls don't exceed the maximum
supported size or throughput by specifying the maximum number of records that GetRecords can return in the Limit parameter. Consider your average record
size when determining this limit. For example, if your average record size is
40 KB, you can limit the data returned to about 1 MB per call by specifying
25 as the limit.

The size of the data returned by GetRecords will vary depending on the
utilization of the shard. The maximum size of data that GetRecords can return
is 10 MB. If a call returns 10 MB of data, subsequent calls made within the
next 5 seconds throw ProvisionedThroughputExceededException. If there is
insufficient provisioned throughput on the shard, subsequent calls made
within the next 1 second throw ProvisionedThroughputExceededException. Note
that GetRecords won't return any data when it throws an exception. For this
reason, we recommend that you wait one second between calls to GetRecords;
however, it's possible that the application will get exceptions for longer
than 1 second.

To detect whether the application is falling behind in processing, add a
timestamp to your records and note how long it takes to process them. You can
also monitor how much data is in a stream using the CloudWatch metrics for PutRecord. For more information, see Monitoring Amazon Kinesis with Amazon CloudWatch
in the Amazon Kinesis Developer Guide.